CLASSIFICATION OF AMERICAN WHEAT VARIETIES. 25 
also certain varieties of wheat which are not homozygous as to winter 
or spring habit. The habit of groAvth is determined by sowing the 
wheat in the spring and observing its behavior. A winter wheat is 
one which usually produces no seed when sown at the normal date of 
seeding for spring wheat. All varieties classed as winter wheats in the 
key can be successfully produced only from fall sowing. When spring 
sown they usually remain prostrate on the ground throughout the 
growing season and produce no culms or spikes. In some sections, 
or in some years, or when sown very early, winter-wheat varieties 
when spring sown will head and produce seed, but this usually occurs 
very late in the season. 
All varieties of wheat classified as spring wheats can be success- 
fully grown from fall sowing only in mild climates, such as the 
southern parts of the United States and along the Pacific coast. Iq 
parts of this territory they will sometimes winterkill. When spring 
sown their early growth is erect and culms and spikes are produced 
during the early part of the growing season. 
TIME OF MATUEITY. 
The time between emergence and maturity is often an important 
economic factor in wheat production. The duration of the growing 
period is indicated by classing varieties as early or midseason or late. 
These are considered secondary characters, but nevertheless are im- 
portant economically and also in classification. Winter wheats and 
spring wheats require periods for growth which can not be directly 
compared in number of days. Fall-sown spring wheats may mature 
as late as or later than many of the true winter wheats. The above 
separation, however, into three classes can be used for both fall and 
spring wheats, or for all wheats Avhen sown in the fall. No definite 
unit of time is used, therefore, in defining these separations. It is 
simply a relative measurement to be used in comparing varieties with 
those of which the normal time of maturity is known. Spring 
varieties grown in the northern Great Plains area would be classi- 
fied as early when maturing in 85 to 95 days after emergence, as mid- 
season when maturing in 90 to 100 days, and as late when maturing 
in 95 to 105 days. These variations are so small and such differences 
between the varieties are apparent during so short a period that these 
factors are of minor value in classification and are used only to 
separate closely related varieties. 
TILLERING. 
The tillering or stooling of wheat also is of little taxonomic value 
in separating varieties. Koernicke and Werner {133) recorded the 
number of plants and culms obtained from definite quantities of seed. 
